Numbers up for dopamine myth

I’ve just read an elegant study on the neuroscience of gambling that wonderfully illustrates why the dopamine equals pleasure myth, so often thrown around by the media, is too tired to be useful.

I have seen countless news reports that claim that some activity or other causes dopamine to be released; that dopamine is the ‘pleasure chemical'; and that it’s also released by ‘drugs’, ‘sex’, ‘gambling’ and ‘chocolate’ (a quartet I have named the four dopamen of the neurocalypse).

Normally, this breathless attempt to make something sound sexy is followed by a slightly sinister bit where they say that this dopamine activity is also likely to make it ‘addictive’.

And herein lies the subtlety. Our best evidence tells us that while the dopamine system has many functions, it’s not really a reward system – it’s most likely a reward expectancy system of some kind. Theories of exactly what form this takes differ in the details, but it certainly seems to be active when we’re expecting a reward, whether it actually turns up or not.

The study on gambling, led by neuroscientist Luke Clark, demonstrates that this is true even when the actual experience is unpleasant.

The research team looked at the activity differences in the dopamine-rich mesolimbic system in a gambling task – comparing wins, misses and near-misses. Near-misses were where the reels on a slot machine just missed the payout.

It turns out that near-misses activate almost exactly the same dopamine circuits as actual wins – but here’s the punchline – they were subjectively experienced as the most unpleasant outcome, even worse than total misses.

In other words, the dopamine system was firing like a rocket display but the experience was awful.

Interestingly, although near-misses were experienced as aversive they increased the desire to play the game but only when the person had some perception of control, by choosing what the ‘lucky’ picture would be.

Of course, like choosing ‘heads or tails’, it’s only an illusion of control because the outcome is random anyway.

But because of reward expectancy the dopamine system is most active when we think we can control the outcome and modify our strategy next time, even if that sense of control is completely false.

Link to full-text of study on near-misses and dopamine.Link to good coverage of study from Quirks and Quarks.

7 Comments

If dopamine is just about expectancy, how would you explain the pleasure (briefly) evoked by e.g. amphetamine? I mean the pure experience of pleasure, not the salience-related effects. This is not a rhetorical question, I’m really wondering.

If dopamine is just about expectancy, how would you explain the pleasure (briefly) evoked by e.g. amphetamine? I mean the pure experience of pleasure, not the salience-related effects. This is not a rhetorical question, I’m really wondering.

Spamham: I think you are illustrating just the issue that the post addresses. You are presuming that the euphoria produced by drugs is caused by dopamine. Given the correlation, it has become all too common to assume causation. The question “if not dopamine, then what causes it?” is not a question that needs to be answered for us to know that it is not dopamine.

tmaxPA:
I’m assuming no such thing. If I had said “drugs in general”, you’d have a point. To my knowledge, amphetamine is pretty specific for dopamine and noadrenaline, with a bit of serotonin activity thrown in. Now, drugs which are serotonin/noradrenaline, but not dopamine, reuptake inhibitors or releasers don’t evoke immediate pleasure in any compareable sense (for example, some antidepressants fit that category).
Maybe amphetamine has effects at some additional sites, but isn’t it safe to say that the *intersection* of the mechanisms of actions of the psychostimulants is just dopamine, noradrenaline and serotonin? (Note that I haven’t really researched that question). Now, with serotonin and noradrenaline being ruled out as sufficient causes by themselves, wouldn’t you say we have evidence for (this mode of) dopamine release *causing* the psychostimulant type of pleasure?